1. Field of the Invention
This invention relates to apparatus with micromachined silicon sensors or Micro Electro Mechanical Systems (MEMS) mass flow sensing technology that measures the city gas in the utility industry that requires custody transfer or tariff. This invention also provides the design and make of an independent metrology unit in apparatus that serves for the utility industry such that maintenance service can be performed on-site without separation of the apparatus from the service line.
2. Description of the Related Art
Gas meters for city gas metrology or custody transfer have been dominated by mechanical technology such as turbine, rotary and diaphragm meters. These meters have been on market for over 160 years enjoying a long service life and reliability. However, these mechanical technologies measure only volumetric changes of the gas and additional apparatus for temperature and pressure measurement are required in order to compensate the significant metrology impact due to the environmental variations of temperature and pressure. For example, for a volumetric mechanical gas meter, every 10 Celsius degree variation of the environmental temperature will lead to 3% deviation of the measured volumetric value for city gas which is either unfair to the end users or a loss for the gas suppliers based on the single volumetric unit price. Alternative practice adopted by some of the current gas suppliers using a nominal “thermo” value that in fact is arbitrary to the users. Since earlier 1980s, many efforts have been made for an all-electronic gas meter that shall have the capability of compensate the variation of temperature and pressure as well as the capability for remote data communication and data safety. The earlier development of the all-electronic ultrasonic gas meters in 1980s, for example, by Taphorn et al. (W. Taphorn et al., Ultrasonic gas meter. U.S. Pat. No. 5,433,117) had been successfully leading to the electronic gas meters in deployment. But the cost of such has up to date prevented it from large scale installation in the field. Pearman et al. (A. N. J. Pearman et al, Electronic gas meter, U.S. Pat. No. 4,918,995) teaches an electronic gas meter using a MEMS mass flow sensor that shall have the automatic temperature and pressure compensation. But the pattern does not lead to a commercialization. Matter (D. Matter et al., Increased accuracy gas energy meter, U.S. Pat. No. 7,222,028) proposed a new electronic gas meter with a MEMS mass flow sensor integrated with application specific integrated circuitry. Such a meter can not only measure the flow rate but the gas energy. The prototype based on this pattern had been fabricated but commercialization is not achieved as of today because of no acceptable metrology standards are available. In addition, the design of as by-pass flow sensing channel in the order of a couple of mini-meters in diameter also led to speculations of possible losing of metrology due to contamination or particles in the flow medium. Muraoka et al. (Muraoka et al, Flowmeter, U.S. Pat. No. 7,861,585) disclosed an electronic gas meter with dual MEMS sensors for large flow measurement, and the meters fabricated have been used in some industrial applications, but due to the design has as high pressure drop, applications in city gas metrology could not be realized.
Wang et al. (Wang et al., Micromachined mass flow sensor and insertion type flow meters and manufacture methods, U.S. Pat. No. 7,536,908) teaches an apparatus fur gas flow measurement utilizing a MEMS mass flow sensor. It is an all-electronic gas meter with full capability of data safety and remote communications and the meters fabricated accordingly have been made commercially available for city gas metrology since 2007. This type of the MEMS gas meters for city gas metrology has provided direct measurement of the gas flow in the flow pipelines and solved the critical issues for the gas metrology with huge dynamic measurement ranges as well as battery powered electronics. The meter designed is of a direct flow pass through without any possibilities of clogging such that it has a better performance as compared to the rotary meters as particle clogging would shut off the gas supply with the rotary meters leading to detrimental results in industrial processing lines such as ceramic making. However, for many practical cases, in case of malfunctioning the electronic meters it often requires services at factory or service centers of the original manufacture instead of onsite part clean or replacement with sonic of the mechanical meters such as rotary meters or turbine. In addition, as the city gas meters are often tied up with the custody transfer metrology and tariff regulations, annual or biannual inspection/services are often mandatory, the return of the whole meter to the factory or the service centers would inigate customer complains of service disruption, bill dispute and/or other inconveniences, the problems now exist also with the current mechanical meter technologies. Further, it is also a costly procedure for both customers and manufacturers.
Therewith it is desired for this invention that the MEMS based electronic meter shall have the capability to provide continued metrology services while onsite repair or the regular services or maintenance is required. This continuation of services of the desired all-electronic gas meters shall also include the mandatory change or dismantlement of metrology units or any parts with the capability of maintaining the metrology integrate.